Abstract. The global carbon budget of terrestrial ecosystems is
chiefly determined by major flows of carbon dioxide (CO2) such as
photosynthesis and respiration, but various minor flows exert considerable
influence in determining carbon stocks and their turnover. This study
assessed the effects of eight minor carbon flows on the terrestrial carbon
budget using a process-based model, the Vegetation Integrative SImulator for
Trace gases (VISIT), which included non-CO2 carbon flows, such as
methane and biogenic volatile organic compound (BVOC) emissions and
subsurface carbon exports and disturbances such as biomass burning, land-use
changes, and harvest activities. The range of model-associated uncertainty
was evaluated through parameter-ensemble simulations and the results were
compared with corresponding observational and modeling studies. In the
historical period of 1901–2016, the VISIT simulation indicated that the
minor flows substantially influenced terrestrial carbon stocks, flows, and
budgets. The simulations estimated mean net ecosystem production in 2000–2009 as 3.21±1.1 Pg C yr−1 without minor flows and 6.85±0.9 Pg C yr−1 with minor flows. Including minor carbon flows
yielded an estimated net biome production of 1.62±1.0 Pg C yr−1
in the same period. Biomass burning, wood harvest, export of organic carbon
by water erosion, and BVOC emissions had impacts on the global terrestrial
carbon budget amounting to around 1 Pg C yr−1 with specific interannual variabilities. After including the minor flows, ecosystem carbon storage was
suppressed by about 440 Pg C, and its mean residence time was shortened by
about 2.4 years. The minor flows occur heterogeneously over the land, such that
BVOC emission, subsurface export, and wood harvest occur mainly in the
tropics, and biomass burning occurs extensively in boreal forests. They also
differ in their decadal trends, due to differences in their driving factors.
Aggregating the simulation results by land-cover type, cropland fraction,
and annual precipitation yielded more insight into the contributions of
these minor flows to the terrestrial carbon budget. Considering their
substantial and unique roles, these minor flows should be taken into account
in the global carbon budget in an integrated manner.
Decadal Variability in the Terrestrial Carbon Budget Caused by the Pacific Decadal Oscillation and Atlantic Multidecadal Oscillation
